/*   Innobase relational database engine; Copyright (C) 2001 Innobase Oy

     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License 2
     as published by the Free Software Foundation in June 1991.

     This program is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     GNU General Public License for more details.

     You should have received a copy of the GNU General Public License 2
     along with this program (in file COPYING); if not, write to the Free
     Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */
/******************************************************
The database buffer pool high-level routines

(c) 1995 Innobase Oy

Created 11/5/1995 Heikki Tuuri
*******************************************************/

#ifndef buf0buf_h
#define buf0buf_h

#include "univ.i"
#include "fil0fil.h"
#include "mtr0types.h"
#include "buf0types.h"
#include "sync0rw.h"
#include "hash0hash.h"
#include "ut0byte.h"
#include "os0proc.h"

/* Flags for flush types */
#define BUF_FLUSH_LRU 1
#define BUF_FLUSH_SINGLE_PAGE 2
#define BUF_FLUSH_LIST                  \
  3 /* An array in the pool struct      \
    has size BUF_FLUSH_LIST + 1: if you \
    add more flush types, put them in   \
    the middle! */
/* Modes for buf_page_get_gen */
#define BUF_GET 10            /* get always */
#define BUF_GET_IF_IN_POOL 11 /* get if in pool */
#define BUF_GET_NOWAIT                   \
  12 /* get if can set the latch without \
     waiting */
#define BUF_GET_NO_LATCH                     \
  14 /* get and bufferfix, but set no latch; \
     we have separated this case, because    \
     it is error-prone programming not to    \
     set a latch, and it should be used      \
     with care */
/* Modes for buf_page_get_known_nowait */
#define BUF_MAKE_YOUNG 51
#define BUF_KEEP_OLD 52
/* Magic value to use instead of checksums when they are disabled */
#define BUF_NO_CHECKSUM_MAGIC 0xDEADBEEFUL

extern buf_pool_t *buf_pool; /* The buffer pool of the database */
#ifdef UNIV_DEBUG
extern ibool buf_debug_prints;            /* If this is set TRUE, the program
                                         prints info whenever read or flush
                                         occurs */
#endif                                    /* UNIV_DEBUG */
extern ulint srv_buf_pool_write_requests; /* variable to count write request
                                          issued */

/************************************************************************
Creates the buffer pool. */

buf_pool_t *buf_pool_init(
    /*==========*/
    /* out, own: buf_pool object, NULL if not
    enough memory or error */
    ulint max_size,  /* in: maximum size of the buf_pool in
                     blocks */
    ulint curr_size, /* in: current size to use, must be <=
                     max_size, currently must be equal to
                     max_size */
    ulint n_frames); /* in: number of frames; if AWE is used,
                     this is the size of the address space window
                     where physical memory pages are mapped; if
                     AWE is not used then this must be the same
                     as max_size */
/*************************************************************************
Gets the current size of buffer buf_pool in bytes. In the case of AWE, the
size of AWE window (= the frames). */
UNIV_INLINE
ulint buf_pool_get_curr_size(void);
/*========================*/
/* out: size in bytes */
/*************************************************************************
Gets the maximum size of buffer pool in bytes. In the case of AWE, the
size of AWE window (= the frames). */
UNIV_INLINE
ulint buf_pool_get_max_size(void);
/*=======================*/
/* out: size in bytes */
/************************************************************************
Gets the smallest oldest_modification lsn for any page in the pool. Returns
ut_dulint_zero if all modified pages have been flushed to disk. */
UNIV_INLINE
dulint buf_pool_get_oldest_modification(void);
/*==================================*/
/* out: oldest modification in pool,
ut_dulint_zero if none */
/*************************************************************************
Allocates a buffer frame. */

buf_frame_t *buf_frame_alloc(void);
/*==================*/
/* out: buffer frame */
/*************************************************************************
Frees a buffer frame which does not contain a file page. */

void buf_frame_free(
    /*===========*/
    buf_frame_t *frame); /* in: buffer frame */
/*************************************************************************
Copies contents of a buffer frame to a given buffer. */
UNIV_INLINE
byte *buf_frame_copy(
    /*===========*/
    /* out: buf */
    byte *buf,           /* in: buffer to copy to */
    buf_frame_t *frame); /* in: buffer frame */
/******************************************************************
NOTE! The following macros should be used instead of buf_page_get_gen,
to improve debugging. Only values RW_S_LATCH and RW_X_LATCH are allowed
in LA! */
#define buf_page_get(SP, OF, LA, MTR) buf_page_get_gen(SP, OF, LA, NULL, BUF_GET, __FILE__, __LINE__, MTR)
/******************************************************************
Use these macros to bufferfix a page with no latching. Remember not to
read the contents of the page unless you know it is safe. Do not modify
the contents of the page! We have separated this case, because it is
error-prone programming not to set a latch, and it should be used
with care. */
#define buf_page_get_with_no_latch(SP, OF, MTR) \
  buf_page_get_gen(SP, OF, RW_NO_LATCH, NULL, BUF_GET_NO_LATCH, __FILE__, __LINE__, MTR)
/******************************************************************
NOTE! The following macros should be used instead of buf_page_get_gen, to
improve debugging. Only values RW_S_LATCH and RW_X_LATCH are allowed as LA! */
#define buf_page_get_nowait(SP, OF, LA, MTR) buf_page_get_gen(SP, OF, LA, NULL, BUF_GET_NOWAIT, __FILE__, __LINE__, MTR)
/******************************************************************
NOTE! The following macros should be used instead of
buf_page_optimistic_get_func, to improve debugging. Only values RW_S_LATCH and
RW_X_LATCH are allowed as LA! */
#define buf_page_optimistic_get(LA, BL, G, MC, MTR) buf_page_optimistic_get_func(LA, BL, G, MC, __FILE__, __LINE__, MTR)
/************************************************************************
This is the general function used to get optimistic access to a database
page. */

ibool buf_page_optimistic_get_func(
    /*=========================*/
    /* out: TRUE if success */
    ulint rw_latch,      /* in: RW_S_LATCH, RW_X_LATCH */
    buf_block_t *block,  /* in: guessed block */
    buf_frame_t *guess,  /* in: guessed frame; note that AWE may move
                         frames */
    dulint modify_clock, /* in: modify clock value if mode is
                    ..._GUESS_ON_CLOCK */
    const char *file,    /* in: file name */
    ulint line,          /* in: line where called */
    mtr_t *mtr);         /* in: mini-transaction */
/************************************************************************
Tries to get the page, but if file io is required, releases all latches
in mtr down to the given savepoint. If io is required, this function
retrieves the page to buffer buf_pool, but does not bufferfix it or latch
it. */
UNIV_INLINE
buf_frame_t *buf_page_get_release_on_io(
    /*=======================*/
    /* out: pointer to the frame, or NULL
    if not in buffer buf_pool */
    ulint space,        /* in: space id */
    ulint offset,       /* in: offset of the page within space
                        in units of a page */
    buf_frame_t *guess, /* in: guessed frame or NULL */
    ulint rw_latch,     /* in: RW_X_LATCH, RW_S_LATCH,
                        or RW_NO_LATCH */
    ulint savepoint,    /* in: mtr savepoint */
    mtr_t *mtr);        /* in: mtr */
/************************************************************************
This is used to get access to a known database page, when no waiting can be
done. */

ibool buf_page_get_known_nowait(
    /*======================*/
    /* out: TRUE if success */
    ulint rw_latch,     /* in: RW_S_LATCH, RW_X_LATCH */
    buf_frame_t *guess, /* in: the known page frame */
    ulint mode,         /* in: BUF_MAKE_YOUNG or BUF_KEEP_OLD */
    const char *file,   /* in: file name */
    ulint line,         /* in: line where called */
    mtr_t *mtr);        /* in: mini-transaction */
/************************************************************************
This is the general function used to get access to a database page. */

buf_frame_t *buf_page_get_gen(
    /*=============*/
    /* out: pointer to the frame or NULL */
    ulint space,        /* in: space id */
    ulint offset,       /* in: page number */
    ulint rw_latch,     /* in: RW_S_LATCH, RW_X_LATCH, RW_NO_LATCH */
    buf_frame_t *guess, /* in: guessed frame or NULL */
    ulint mode,         /* in: BUF_GET, BUF_GET_IF_IN_POOL,
                        BUF_GET_NO_LATCH */
    const char *file,   /* in: file name */
    ulint line,         /* in: line where called */
    mtr_t *mtr);        /* in: mini-transaction */
/************************************************************************
Initializes a page to the buffer buf_pool. The page is usually not read
from a file even if it cannot be found in the buffer buf_pool. This is one
of the functions which perform to a block a state transition NOT_USED =>
FILE_PAGE (the other is buf_page_init_for_read above). */

buf_frame_t *buf_page_create(
    /*============*/
    /* out: pointer to the frame, page bufferfixed */
    ulint space,  /* in: space id */
    ulint offset, /* in: offset of the page within space in units of
                  a page */
    mtr_t *mtr);  /* in: mini-transaction handle */
/************************************************************************
Inits a page to the buffer buf_pool, for use in ibbackup --restore. */

void buf_page_init_for_backup_restore(
    /*=============================*/
    ulint space,         /* in: space id */
    ulint offset,        /* in: offset of the page within space
                         in units of a page */
    buf_block_t *block); /* in: block to init */
/************************************************************************
Decrements the bufferfix count of a buffer control block and releases
a latch, if specified. */
UNIV_INLINE
void buf_page_release(
    /*=============*/
    buf_block_t *block, /* in: buffer block */
    ulint rw_latch,     /* in: RW_S_LATCH, RW_X_LATCH,
                        RW_NO_LATCH */
    mtr_t *mtr);        /* in: mtr */
/************************************************************************
Moves a page to the start of the buffer pool LRU list. This high-level
function can be used to prevent an important page from from slipping out of
the buffer pool. */

void buf_page_make_young(
    /*=================*/
    buf_frame_t *frame); /* in: buffer frame of a file page */
/************************************************************************
Returns TRUE if the page can be found in the buffer pool hash table. NOTE
that it is possible that the page is not yet read from disk, though. */

ibool buf_page_peek(
    /*==========*/
    /* out: TRUE if found from page hash table,
    NOTE that the page is not necessarily yet read
    from disk! */
    ulint space,   /* in: space id */
    ulint offset); /* in: page number */
/************************************************************************
Returns the buffer control block if the page can be found in the buffer
pool. NOTE that it is possible that the page is not yet read
from disk, though. This is a very low-level function: use with care! */

buf_block_t *buf_page_peek_block(
    /*================*/
    /* out: control block if found from page hash table,
    otherwise NULL; NOTE that the page is not necessarily
    yet read from disk! */
    ulint space,   /* in: space id */
    ulint offset); /* in: page number */
/************************************************************************
Resets the check_index_page_at_flush field of a page if found in the buffer
pool. */

void buf_reset_check_index_page_at_flush(
    /*================================*/
    ulint space,   /* in: space id */
    ulint offset); /* in: page number */
/************************************************************************
Sets file_page_was_freed TRUE if the page is found in the buffer pool.
This function should be called when we free a file page and want the
debug version to check that it is not accessed any more unless
reallocated. */

buf_block_t *buf_page_set_file_page_was_freed(
    /*=============================*/
    /* out: control block if found from page hash table,
    otherwise NULL */
    ulint space,   /* in: space id */
    ulint offset); /* in: page number */
/************************************************************************
Sets file_page_was_freed FALSE if the page is found in the buffer pool.
This function should be called when we free a file page and want the
debug version to check that it is not accessed any more unless
reallocated. */

buf_block_t *buf_page_reset_file_page_was_freed(
    /*===============================*/
    /* out: control block if found from page hash table,
    otherwise NULL */
    ulint space,   /* in: space id */
    ulint offset); /* in: page number */
/************************************************************************
Recommends a move of a block to the start of the LRU list if there is danger
of dropping from the buffer pool. NOTE: does not reserve the buffer pool
mutex. */
UNIV_INLINE
ibool buf_block_peek_if_too_old(
    /*======================*/
    /* out: TRUE if should be made younger */
    buf_block_t *block); /* in: block to make younger */
/************************************************************************
Returns the current state of is_hashed of a page. FALSE if the page is
not in the pool. NOTE that this operation does not fix the page in the
pool if it is found there. */

ibool buf_page_peek_if_search_hashed(
    /*===========================*/
    /* out: TRUE if page hash index is built in search
    system */
    ulint space,   /* in: space id */
    ulint offset); /* in: page number */
/************************************************************************
Gets the youngest modification log sequence number for a frame.
Returns zero if not file page or no modification occurred yet. */
UNIV_INLINE
dulint buf_frame_get_newest_modification(
    /*==============================*/
    /* out: newest modification to page */
    buf_frame_t *frame); /* in: pointer to a frame */
/************************************************************************
Increments the modify clock of a frame by 1. The caller must (1) own the
pool mutex and block bufferfix count has to be zero, (2) or own an x-lock
on the block. */
UNIV_INLINE
dulint buf_frame_modify_clock_inc(
    /*=======================*/
    /* out: new value */
    buf_frame_t *frame); /* in: pointer to a frame */
/************************************************************************
Increments the modify clock of a frame by 1. The caller must (1) own the
buf_pool mutex and block bufferfix count has to be zero, (2) or own an x-lock
on the block. */
UNIV_INLINE
dulint buf_block_modify_clock_inc(
    /*=======================*/
    /* out: new value */
    buf_block_t *block); /* in: block */
/************************************************************************
Returns the value of the modify clock. The caller must have an s-lock
or x-lock on the block. */
UNIV_INLINE
dulint buf_block_get_modify_clock(
    /*=======================*/
    /* out: value */
    buf_block_t *block); /* in: block */
/************************************************************************
Calculates a page checksum which is stored to the page when it is written
to a file. Note that we must be careful to calculate the same value
on 32-bit and 64-bit architectures. */

ulint buf_calc_page_new_checksum(
    /*=======================*/
    /* out: checksum */
    byte *page); /* in: buffer page */
/************************************************************************
In versions < 4.0.14 and < 4.1.1 there was a bug that the checksum only
looked at the first few bytes of the page. This calculates that old
checksum.
NOTE: we must first store the new formula checksum to
FIL_PAGE_SPACE_OR_CHKSUM before calculating and storing this old checksum
because this takes that field as an input! */

ulint buf_calc_page_old_checksum(
    /*=======================*/
    /* out: checksum */
    byte *page); /* in: buffer page */
/************************************************************************
Checks if a page is corrupt. */

ibool buf_page_is_corrupted(
    /*==================*/
    /* out: TRUE if corrupted */
    byte *read_buf); /* in: a database page */
/**************************************************************************
Gets the page number of a pointer pointing within a buffer frame containing
a file page. */
UNIV_INLINE
ulint buf_frame_get_page_no(
    /*==================*/
    /* out: page number */
    byte *ptr); /* in: pointer to within a buffer frame */
/**************************************************************************
Gets the space id of a pointer pointing within a buffer frame containing a
file page. */
UNIV_INLINE
ulint buf_frame_get_space_id(
    /*===================*/
    /* out: space id */
    byte *ptr); /* in: pointer to within a buffer frame */
/**************************************************************************
Gets the space id, page offset, and byte offset within page of a
pointer pointing to a buffer frame containing a file page. */
UNIV_INLINE
void buf_ptr_get_fsp_addr(
    /*=================*/
    byte *ptr,         /* in: pointer to a buffer frame */
    ulint *space,      /* out: space id */
    fil_addr_t *addr); /* out: page offset and byte offset */
/**************************************************************************
Gets the hash value of the page the pointer is pointing to. This can be used
in searches in the lock hash table. */
UNIV_INLINE
ulint buf_frame_get_lock_hash_val(
    /*========================*/
    /* out: lock hash value */
    byte *ptr); /* in: pointer to within a buffer frame */
/**************************************************************************
Gets the mutex number protecting the page record lock hash chain in the lock
table. */
UNIV_INLINE
mutex_t *buf_frame_get_lock_mutex(
    /*=====================*/
    /* out: mutex */
    byte *ptr); /* in: pointer to within a buffer frame */
/***********************************************************************
Gets the frame the pointer is pointing to. */
UNIV_INLINE
buf_frame_t *buf_frame_align(
    /*============*/
    /* out: pointer to frame */
    byte *ptr); /* in: pointer to a frame */
/***********************************************************************
Checks if a pointer points to the block array of the buffer pool (blocks, not
the frames). */
UNIV_INLINE
ibool buf_pool_is_block(
    /*==============*/
    /* out: TRUE if pointer to block */
    void *ptr); /* in: pointer to memory */
#ifdef UNIV_DEBUG
/*************************************************************************
Validates the buffer pool data structure. */

ibool buf_validate(void);
/*==============*/
/*************************************************************************
Prints info of the buffer pool data structure. */

void buf_print(void);
/*============*/
#endif /* UNIV_DEBUG */
/************************************************************************
Prints a page to stderr. */

void buf_page_print(
    /*===========*/
    byte *read_buf); /* in: a database page */
/*************************************************************************
Returns the number of latched pages in the buffer pool. */

ulint buf_get_latched_pages_number(void);
/*==============================*/
/*************************************************************************
Returns the number of pending buf pool ios. */

ulint buf_get_n_pending_ios(void);
/*=======================*/
/*************************************************************************
Prints info of the buffer i/o. */

void buf_print_io(
    /*=========*/
    FILE *file); /* in: file where to print */
/*************************************************************************
Returns the ratio in percents of modified pages in the buffer pool /
database pages in the buffer pool. */

ulint buf_get_modified_ratio_pct(void);
/*============================*/
/**************************************************************************
Refreshes the statistics used to print per-second averages. */

void buf_refresh_io_stats(void);
/*======================*/
/*************************************************************************
Checks that all file pages in the buffer are in a replaceable state. */

ibool buf_all_freed(void);
/*===============*/
/*************************************************************************
Checks that there currently are no pending i/o-operations for the buffer
pool. */

ibool buf_pool_check_no_pending_io(void);
/*==============================*/
/* out: TRUE if there is no pending i/o */
/*************************************************************************
Invalidates the file pages in the buffer pool when an archive recovery is
completed. All the file pages buffered must be in a replaceable state when
this function is called: not latched and not modified. */

void buf_pool_invalidate(void);
/*=====================*/

/*========================================================================
--------------------------- LOWER LEVEL ROUTINES -------------------------
=========================================================================*/

/************************************************************************
Maps the page of block to a frame, if not mapped yet. Unmaps some page
from the end of the awe_LRU_free_mapped. */

void buf_awe_map_page_to_frame(
    /*======================*/
    buf_block_t *block,        /* in: block whose page should be
                               mapped to a frame */
    ibool add_to_mapped_list); /* in: TRUE if we in the case
                           we need to map the page should also
                           add the block to the
                           awe_LRU_free_mapped list */
#ifdef UNIV_SYNC_DEBUG
/*************************************************************************
Adds latch level info for the rw-lock protecting the buffer frame. This
should be called in the debug version after a successful latching of a
page if we know the latching order level of the acquired latch. */
UNIV_INLINE
void buf_page_dbg_add_level(
    /*===================*/
    buf_frame_t *frame, /* in: buffer page where we have acquired
                        a latch */
    ulint level);       /* in: latching order level */
#endif                  /* UNIV_SYNC_DEBUG */
/*************************************************************************
Gets a pointer to the memory frame of a block. */
UNIV_INLINE
buf_frame_t *buf_block_get_frame(
    /*================*/
    /* out: pointer to the frame */
    buf_block_t *block); /* in: pointer to the control block */
/*************************************************************************
Gets the space id of a block. */
UNIV_INLINE
ulint buf_block_get_space(
    /*================*/
    /* out: space id */
    buf_block_t *block); /* in: pointer to the control block */
/*************************************************************************
Gets the page number of a block. */
UNIV_INLINE
ulint buf_block_get_page_no(
    /*==================*/
    /* out: page number */
    buf_block_t *block); /* in: pointer to the control block */
/***********************************************************************
Gets the block to whose frame the pointer is pointing to. */
UNIV_INLINE
buf_block_t *buf_block_align(
    /*============*/
    /* out: pointer to block */
    byte *ptr); /* in: pointer to a frame */
/************************************************************************
This function is used to get info if there is an io operation
going on on a buffer page. */
UNIV_INLINE
ibool buf_page_io_query(
    /*==============*/
    /* out: TRUE if io going on */
    buf_block_t *block); /* in: pool block, must be bufferfixed */
/***********************************************************************
Accessor function for block array. */
UNIV_INLINE
buf_block_t *buf_pool_get_nth_block(
    /*===================*/
    /* out: pointer to block */
    buf_pool_t *pool, /* in: pool */
    ulint i);         /* in: index of the block */
/************************************************************************
Function which inits a page for read to the buffer buf_pool. If the page is
(1) already in buf_pool, or
(2) if we specify to read only ibuf pages and the page is not an ibuf page, or
(3) if the space is deleted or being deleted,
then this function does nothing.
Sets the io_fix flag to BUF_IO_READ and sets a non-recursive exclusive lock
on the buffer frame. The io-handler must take care that the flag is cleared
and the lock released later. This is one of the functions which perform the
state transition NOT_USED => FILE_PAGE to a block (the other is
buf_page_create). */

buf_block_t *buf_page_init_for_read(
    /*===================*/
    /* out: pointer to the block or NULL */
    ulint *err,                     /* out: DB_SUCCESS or DB_TABLESPACE_DELETED */
    ulint mode,                     /* in: BUF_READ_IBUF_PAGES_ONLY, ... */
    ulint space,                    /* in: space id */
    ib_longlong tablespace_version, /* in: prevents reading from a wrong
                         version of the tablespace in case we have done
                         DISCARD + IMPORT */
    ulint offset);                  /* in: page number */
/************************************************************************
Completes an asynchronous read or write request of a file page to or from
the buffer pool. */

void buf_page_io_complete(
    /*=================*/
    buf_block_t *block); /* in: pointer to the block in question */
/************************************************************************
Calculates a folded value of a file page address to use in the page hash
table. */
UNIV_INLINE
ulint buf_page_address_fold(
    /*==================*/
    /* out: the folded value */
    ulint space,   /* in: space id */
    ulint offset); /* in: offset of the page within space */
/**********************************************************************
Returns the control block of a file page, NULL if not found. */
UNIV_INLINE
buf_block_t *buf_page_hash_get(
    /*==============*/
    /* out: block, NULL if not found */
    ulint space,   /* in: space id */
    ulint offset); /* in: offset of the page within space */
/***********************************************************************
Increments the pool clock by one and returns its new value. Remember that
in the 32 bit version the clock wraps around at 4 billion! */
UNIV_INLINE
ulint buf_pool_clock_tic(void);
/*====================*/
/* out: new clock value */
/*************************************************************************
Gets the current length of the free list of buffer blocks. */

ulint buf_get_free_list_len(void);
/*=======================*/

/* The buffer control block structure */

struct buf_block_struct
{
  /* 1. General fields */

  ulint magic_n;       /* magic number to check */
  ulint state;         /* state of the control block:
                       BUF_BLOCK_NOT_USED, ... */
  byte *frame;         /* pointer to buffer frame which
                       is of size UNIV_PAGE_SIZE, and
                       aligned to an address divisible by
                       UNIV_PAGE_SIZE; if AWE is used, this
                       will be NULL for the pages which are
                       currently not mapped into the virtual
                       address space window of the buffer
                       pool */
  os_awe_t *awe_info;  /* if AWE is used, then an array of
                       awe page infos for
                       UNIV_PAGE_SIZE / OS_AWE_X86_PAGE_SIZE
                       (normally = 4) physical memory
                       pages; otherwise NULL */
  ulint space;         /* space id of the page */
  ulint offset;        /* page number within the space */
  ulint lock_hash_val; /* hashed value of the page address
                       in the record lock hash table */
  mutex_t *lock_mutex; /* mutex protecting the chain in the
                       record lock hash table */
  rw_lock_t lock;      /* read-write lock of the buffer
                       frame */
  buf_block_t *hash;   /* node used in chaining to the page
                       hash table */
  ibool check_index_page_at_flush;
  /* TRUE if we know that this is
  an index page, and want the database
  to check its consistency before flush;
  note that there may be pages in the
  buffer pool which are index pages,
  but this flag is not set because
  we do not keep track of all pages */
  dict_index_t *index; /* index for which the adaptive
                       hash index has been created */
  /* 2. Page flushing fields */

  UT_LIST_NODE_T(buf_block_t) flush_list;
  /* node of the modified, not yet
  flushed blocks list */
  dulint newest_modification;
  /* log sequence number of the youngest
  modification to this block, zero if
  not modified */
  dulint oldest_modification;
  /* log sequence number of the START of
  the log entry written of the oldest
  modification to this block which has
  not yet been flushed on disk; zero if
  all modifications are on disk */
  ulint flush_type; /* if this block is currently being
                    flushed to disk, this tells the
                    flush_type: BUF_FLUSH_LRU or
                    BUF_FLUSH_LIST */

  /* 3. LRU replacement algorithm fields */

  UT_LIST_NODE_T(buf_block_t) free;
  /* node of the free block list */
  ibool in_free_list; /* TRUE if in the free list; used in
                      debugging */
  UT_LIST_NODE_T(buf_block_t) LRU;
  /* node of the LRU list */
  UT_LIST_NODE_T(buf_block_t) awe_LRU_free_mapped;
  /* in the AWE version node in the
  list of free and LRU blocks which are
  mapped to a frame */
  ibool in_LRU_list;      /* TRUE of the page is in the LRU list;
                          used in debugging */
  ulint LRU_position;     /* value which monotonically
                          decreases (or may stay constant if
                          the block is in the old blocks) toward
                          the end of the LRU list, if the pool
                          ulint_clock has not wrapped around:
                          NOTE that this value can only be used
                          in heuristic algorithms, because of
                          the possibility of a wrap-around! */
  ulint freed_page_clock; /* the value of freed_page_clock
                         buffer pool when this block was
                         last time put to the head of the
                         LRU list */
  ibool old;              /* TRUE if the block is in the old
                          blocks in the LRU list */
  ibool accessed;         /* TRUE if the page has been accessed
                          while in the buffer pool: read-ahead
                          may read in pages which have not been
                          accessed yet */
  ulint buf_fix_count;    /* count of how manyfold this block
                          is currently bufferfixed */
  ulint io_fix;           /* if a read is pending to the frame,
                          io_fix is BUF_IO_READ, in the case
                          of a write BUF_IO_WRITE, otherwise 0 */
  /* 4. Optimistic search field */

  dulint modify_clock; /* this clock is incremented every
                       time a pointer to a record on the
                       page may become obsolete; this is
                       used in the optimistic cursor
                       positioning: if the modify clock has
                       not changed, we know that the pointer
                       is still valid; this field may be
                       changed if the thread (1) owns the
                       pool mutex and the page is not
                       bufferfixed, or (2) the thread has an
                       x-latch on the block */

  /* 5. Hash search fields: NOTE that the first 4 fields are NOT
  protected by any semaphore! */

  ulint n_hash_helps; /* counter which controls building
                      of a new hash index for the page */
  ulint n_fields;     /* recommended prefix length for hash
                      search: number of full fields */
  ulint n_bytes;      /* recommended prefix: number of bytes
                      in an incomplete field */
  ulint side;         /* BTR_SEARCH_LEFT_SIDE or
                      BTR_SEARCH_RIGHT_SIDE, depending on
                      whether the leftmost record of several
                      records with the same prefix should be
                      indexed in the hash index */

  /* The following 4 fields are protected by btr_search_latch: */

  ibool is_hashed;     /* TRUE if hash index has already been
                       built on this page; note that it does
                       not guarantee that the index is
                       complete, though: there may have been
                       hash collisions, record deletions,
                       etc. */
  ulint n_pointers;    /* used in debugging: the number of
                       pointers in the adaptive hash index
                       pointing to this frame */
  ulint curr_n_fields; /* prefix length for hash indexing:
                       number of full fields */
  ulint curr_n_bytes;  /* number of bytes in hash indexing */
  ulint curr_side;     /* BTR_SEARCH_LEFT_SIDE or
                       BTR_SEARCH_RIGHT_SIDE in hash
                       indexing */
                       /* 6. Debug fields */
#ifdef UNIV_SYNC_DEBUG
  rw_lock_t debug_latch; /* in the debug version, each thread
                         which bufferfixes the block acquires
                         an s-latch here; so we can use the
                         debug utilities in sync0rw */
#endif
  ibool file_page_was_freed;
  /* this is set to TRUE when fsp
  frees a page in buffer pool */
};

#define BUF_BLOCK_MAGIC_N 41526563

/* The buffer pool structure. NOTE! The definition appears here only for
other modules of this directory (buf) to see it. Do not use from outside! */

struct buf_pool_struct
{
  /* 1. General fields */

  mutex_t mutex;                  /* mutex protecting the buffer pool
                                  struct and control blocks, except the
                                  read-write lock in them */
  byte *frame_mem;                /* pointer to the memory area which
                                  was allocated for the frames; in AWE
                                  this is the virtual address space
                                  window where we map pages stored
                                  in physical memory */
  byte *frame_zero;               /* pointer to the first buffer frame:
                                  this may differ from frame_mem, because
                                  this is aligned by the frame size */
  byte *high_end;                 /* pointer to the end of the buffer
                                  frames */
  ulint n_frames;                 /* number of frames */
  buf_block_t *blocks;            /* array of buffer control blocks */
  buf_block_t **blocks_of_frames; /* inverse mapping which can be used
                                 to retrieve the buffer control block
                                 of a frame; this is an array which
                                 lists the blocks of frames in the
                                 order frame_zero,
                                 frame_zero + UNIV_PAGE_SIZE, ...
                                 a control block is always assigned
                                 for each frame, even if the frame does
                                 not contain any data; note that in AWE
                                 there are more control blocks than
                                 buffer frames */
  os_awe_t *awe_info;             /* if AWE is used, AWE info for the
                                  physical 4 kB memory pages associated
                                  with buffer frames */
  ulint max_size;                 /* number of control blocks ==
                                  maximum pool size in pages */
  ulint curr_size;                /* current pool size in pages;
                                  currently always the same as
                                  max_size */
  hash_table_t *page_hash;        /* hash table of the file pages */

  ulint n_pend_reads; /* number of pending read operations */

  time_t last_printout_time;  /* when buf_print was last time
                          called */
  ulint n_pages_read;         /* number read operations */
  ulint n_pages_written;      /* number write operations */
  ulint n_pages_created;      /* number of pages created in the pool
                              with no read */
  ulint n_page_gets;          /* number of page gets performed;
                              also successful searches through
                              the adaptive hash index are
                              counted as page gets; this field
                              is NOT protected by the buffer
                              pool mutex */
  ulint n_pages_awe_remapped; /* if AWE is enabled, the
                        number of remaps of blocks to
                        buffer frames */
  ulint n_page_gets_old;      /* n_page_gets when buf_print was
                              last time called: used to calculate
                              hit rate */
  ulint n_pages_read_old;     /* n_pages_read when buf_print was
                             last time called */
  ulint n_pages_written_old;  /* number write operations */
  ulint n_pages_created_old;  /* number of pages created in
                          the pool with no read */
  ulint n_pages_awe_remapped_old;
  /* 2. Page flushing algorithm fields */

  UT_LIST_BASE_NODE_T(buf_block_t) flush_list;
  /* base node of the modified block
  list */
  ibool init_flush[BUF_FLUSH_LIST + 1];
  /* this is TRUE when a flush of the
  given type is being initialized */
  ulint n_flush[BUF_FLUSH_LIST + 1];
  /* this is the number of pending
  writes in the given flush type */
  os_event_t no_flush[BUF_FLUSH_LIST + 1];
  /* this is in the set state when there
  is no flush batch of the given type
  running */
  ulint ulint_clock;      /* a sequence number used to count
                          time. NOTE! This counter wraps
                          around at 4 billion (if ulint ==
                          32 bits)! */
  ulint freed_page_clock; /* a sequence number used to count the
                         number of buffer blocks removed from
                         the end of the LRU list; NOTE that
                         this counter may wrap around at 4
                         billion! */
  ulint LRU_flush_ended;  /* when an LRU flush ends for a page,
                          this is incremented by one; this is
                          set to zero when a buffer block is
                          allocated */

  /* 3. LRU replacement algorithm fields */

  UT_LIST_BASE_NODE_T(buf_block_t) free;
  /* base node of the free block list;
  in the case of AWE, at the start are
  always free blocks for which the
  physical memory is mapped to a frame */
  UT_LIST_BASE_NODE_T(buf_block_t) LRU;
  /* base node of the LRU list */
  buf_block_t *LRU_old; /* pointer to the about 3/8 oldest
                        blocks in the LRU list; NULL if LRU
                        length less than BUF_LRU_OLD_MIN_LEN */
  ulint LRU_old_len;    /* length of the LRU list from
                        the block to which LRU_old points
                        onward, including that block;
                        see buf0lru.c for the restrictions
                        on this value; not defined if
                        LRU_old == NULL */
  UT_LIST_BASE_NODE_T(buf_block_t) awe_LRU_free_mapped;
  /* list of those blocks which are
  in the LRU list or the free list, and
  where the page is mapped to a frame;
  thus, frames allocated, e.g., to the
  locki table, are not in this list */
};

/* States of a control block */
#define BUF_BLOCK_NOT_USED 211 /* is in the free list */
#define BUF_BLOCK_READY_FOR_USE                                    \
  212                           /* when buf_get_free_block returns \
                                a block, it is in this state */
#define BUF_BLOCK_FILE_PAGE 213 /* contains a buffered file page */
#define BUF_BLOCK_MEMORY 214    /* contains some main memory object */
#define BUF_BLOCK_REMOVE_HASH         \
  215 /* hash index should be removed \
      before putting to the free list */

/* Io_fix states of a control block; these must be != 0 */
#define BUF_IO_READ 561
#define BUF_IO_WRITE 562

/************************************************************************
Let us list the consistency conditions for different control block states.

NOT_USED:	is in free list, not in LRU list, not in flush list, nor
                page hash table
READY_FOR_USE:	is not in free list, LRU list, or flush list, nor page
                hash table
MEMORY:		is not in free list, LRU list, or flush list, nor page
                hash table
FILE_PAGE:	space and offset are defined, is in page hash table
                if io_fix == BUF_IO_WRITE,
                        pool: no_flush[block->flush_type] is in reset state,
                        pool: n_flush[block->flush_type] > 0

                (1) if buf_fix_count == 0, then
                        is in LRU list, not in free list
                        is in flush list,
                                if and only if oldest_modification > 0
                        is x-locked,
                                if and only if io_fix == BUF_IO_READ
                        is s-locked,
                                if and only if io_fix == BUF_IO_WRITE

                (2) if buf_fix_count > 0, then
                        is not in LRU list, not in free list
                        is in flush list,
                                if and only if oldest_modification > 0
                        if io_fix == BUF_IO_READ,
                                is x-locked
                        if io_fix == BUF_IO_WRITE,
                                is s-locked

State transitions:

NOT_USED => READY_FOR_USE
READY_FOR_USE => MEMORY
READY_FOR_USE => FILE_PAGE
MEMORY => NOT_USED
FILE_PAGE => NOT_USED	NOTE: This transition is allowed if and only if
                                (1) buf_fix_count == 0,
                                (2) oldest_modification == 0, and
                                (3) io_fix == 0.
*/

#ifndef UNIV_NONINL
#include "buf0buf.ic"
#endif

#endif
